Every year corneal opacity blinds or visually impairs thousands of people. The causes of corneal opacity are quite diverse, and consequently the members of the afflicted population suffer a wide range of conditions. Importantly, researchers have identified among the afflicted population, individual patients with corneal opacity that is blinding an otherwise healthy eye. Therefore, a major goal of ophthalmology is to find a treatment that alleviates corneal opacity to restore to these members of the afflicted population their ability to see.
A healthy cornea is an almost perfectly transparent layer of tissue that projects forward from the anterior portion of the eye. The transparent cornea acts like a window that lets light and images enter into the eye, pass through the crystalline lens and project onto the retina.
The retina is positioned at the posterior portion of the eye and at a distance of about one inch from the cornea. The retina is a delicate nervous membrane upon the surface of which the images of external objects are received. The retina is an exceedingly complex structure having many layers of cells and nerve fibers which connect to the optic nerve. It is understood that the retina detects the light and the images that enter the eye through the cornea, and that the images that a person sees are caused by the projected images that stimulate the photoreceptors in the retina.
Although the cornea and the retina are distinct parts of the eye, both parts must function properly for the eye to correctly perceive images. Damage to either the retina or the cornea can impair a person's vision.
Corneal opacity impairs vision by preventing light from reaching the retina. The condition of corneal opacity can arise from a wealth of different situations including trachoma, a chronic and contagious form of conjunctivitis, which is the second most common cause of blindness in the world. Commonly, scarring from abrasive physical contact, chemical exposure, and burning can destroy or damage the corneal tissue and can create scar tissue that turns the cornea opaque or cloudy. In other cases, severe lacrimal fluid deficiency, or dry eye syndrome, can compromise the corneal tissue with scarring. Additionally, infections or severe allergic reactions to various drugs can cause scarring of the lid under surface which, in turn, results in repetitive micro-trauma to the corneal surface. This is a persistent condition that, over the long term, results in corneal scarring and obstructed vision.
Just as the causes of corneal opacity can vary widely, so too can the extent of the scarring and the degeneration. However, regardless of the cause or the extent, the resultant corneal damage can substantially impair the patient's vision. In cases of severe damage the corneal tissue can be permanently and totally impaired, thereby causing blindness in the patient due to insufficient light passing through the cornea. Even in the case of sparse scarring or clouding, the degenerated corneal epithelium can substantially decrease visual acuity.
However, although the patient's vision is lost or substantially impaired due to the damage to the cornea, the patient may still retain a healthy retina and therefore have a significant potential visual acuity. For example, researchers have identified patients who have substantially opaque corneas but are still able to detect light when the light is projected with sufficient intensity against the surface of the damaged cornea. This indicates that the patient has a functioning retina and possibly a significant potential visual acuity. More recently, researchers have identified patients that can "read" a Snellen chart if the chart is projected into the eye by light of sufficient intensity. These tests have been performed to identify the candidate patients whom are likely to benefit from a surgical procedure that could correct the vision impairment caused by the medial opacity, such as a cataract.
Conventional surgical techniques exist for treating the corneal opacity of some patients. Typically, the candidate patient has suffered substantial corneal damage, but the eye in general is well shaped and the retina appears healthy. These techniques, such as cadaveric corneal graft involve surgically removing the damaged cornea and attaching an optical prosthesis, an artificial cornea, to the eye. The optical prosthesis is a transparent membrane that functions just as a healthy cornea, to allow light into the eye.
Although this technique offers help to some patients, it cannot always be practiced on patients who have suffered severe damage to the anterior segment of the eye. Furthermore, the optical prosthesis is extremely prone to extrusion, as it is attached to the outer corneal layer, and is easily sloughed off the eye by occurrences of rejection. Another problem with the optical prosthesis is that tissue can grow over the attached prosthesis, and prevent light from entering the eye. Furthermore, tissue can grow under the prosthesis and block light from the eye, as well as tear the prosthesis from the eye. These and other problems have hampered the use of optical prostheses to bring relief to the afflicted population.
Accordingly, it is an object of the present invention to provide improved systems and methods for alleviating vision impairment caused by corneal opacity.
It is a further object of the present invention to provide medical apparatus and procedures for alleviating corneal opacity that are less affected by the growth of biological tissue.
It is still a further object of the present invention to provide medical apparatus and procedures that are less dependent on the optical properties of a prosthetic device.
It is yet another object of the present invention to provide medical apparatus and procedures that are less affected by the affects of prosthesis extrusion.
It is still another object of the present invention to provide medical apparatus and procedures for alleviating vision impairment caused by corneal opacity in patients having substantial damage to the cornea, the interior portions of the eye, the retina, the optic nerve or other natural optic structure.
These and other general and specific objects of the present invention will become apparent from or appear in the following description of the invention.